Tooling got faster with AI, but the fundamentals did not disappear. If your app feels slow, rough, or heavy to start, you still need to understand what is happening across React, native code, and bundling. This guide puts that context in one place, so teams can spend less time guessing and more time fixing the right thing.

Performance is still product quality. Users do not care whether the issue comes from rendering, memory, startup work, thread usage, or the bundle. They feel it when the app takes too long to become usable, when scrolling gets rough, or when the interface stops responding the way it should.

That is why metrics like TTI and FPS still matter. They give teams a way to connect what users feel to what engineers can actually measure, debug, and improve. When performance slips, the whole experience gets heavier, less stable, and easier to abandon. The good part is that these problems are measurable, and in most cases, fixable once you know where to look.

Who is this guide for?

This guide is for React Native developers, senior engineers, and tech leads. If you're close to the code, it gives you practical ways to profile, debug, and fix the performance problems that surface in everyday work. If you're making broader technical decisions, it gives you a clearer model for startup performance, native bottlenecks, and the tradeoffs behind what is worth fixing first.